Packaged dehydrated potatoes have a shelf life of between 1 and 2 years before they go bad.
Still the dehydrated potatoes are usually good enough to eat after 2 years as long as they've remained sealed however they just won't taste as good or be as fresh.
Also the temperature, humidity and other environmental conditions affect the storage life of dehydrated potatoes but you should be able to keep the dehydrated potatoes for at least 2 years.
If it's been 2 years and you haven't eaten them yet then I would go ahead and eat those dehydrated potatoes and get some fresh dehydrated potatoes to store for emergencies.
Dehydrated potatoes aren't the best eating potatoes but they are good to keep around to have for food in an emergency.
If it has been a year and I still have the dehydrated potatoes I go ahead and use them up and eat them and get some more fresh dehydrated potatoes.
I also make dehydrated potatoes often enough anyway so the ones I keep in my cupboard are mostly eaten up within a week or two and I do keep some in storage just in case I need them for an emergency to eat.